Ion-size effect on normal-state transport properties in R0.8Pr0.2Ba2Cu3O7-y systems (R=Yb, Er, Dy, Gd, Eu, and Nd)

We report detailed studies of the normal-state resistivity and the Hall-effect in bulk R0.8Pr0.2Ba2Cu3O7-y samples (R=Yb, Er, Dy, Gd, Eu, and Nd). We find a linear temperature dependence of the normal-state resistivity ρu and the Hall number nH above Tc in these systems. At a constant temperature both ρn and nH are linearly dependent on the ion-size of the rare earth, viz., the larger R3+ ionic radius, the larger ρn, but the lower nH. The cotangent of the Hall angle follows a universal T2 dependence, i.e., cotθH=αT2+C. Both the slope α and the quantity C is insensitive to the R ion and remains almost constant. On the basis of our data we propose a Tc-nH diagram which manifests an open-quote open-quote underdoping close-quote close-quote behavior of R0.8Pr0.2Ba2Cu3O7-y systems. We suggest that the strong hybridization between the 4f states of the Pr ion and the conduction-band states in CuO2 planes, leading to hole localization and pair breaking, are the mechanism for the suppression of superconductivity in R1-xPrxBa2Cu3O7-y systems. copyright 1996 The American Physical Society